The present invention relates to hang gliding in general and more particularly to a method and to a combination of elements for launching aloft a piloted hang glider by means of an aerial tow consisting of a powered pilotless aircraft remotely controlled from the ground.
Hang gliding is generally considered to be the percursor of modern aviation. George Cayley in England in the middle of the nineteenth century, Otto Lilienthal in Germany and Percy Pilcher in England, at the end of the nineteenth century, practiced hang gliding. Wilbur and Orville Wright's first Flyer was a form of hang glider.
Hang gliding has recently become a very popular sport practiced by many enthusiastic flyers, as a result of the work of Francis M. Rogallo investigating for NASA the use of para-gliders as recovery devices for manned spacecraft. A Rogallo wing is a kite-like structure in the form of a low aspect-ratio delta wing with a simple frame covered by a lightweight material, Dacron or the like, below which is mounted a support harness for the pilot who, by pulling and pushing on a horizontal control bar or trapeze, which is attached by cables or rigid rods to the wing keel and by cables to the tips of the wing, controls the glider in flight by moving his body fore and aft to shift the center of gravity relative to the center of lift of the wing, and sideways for banking and thus turning.
Since the appearance of the Rogallo wing, many other types of hang gliders have been developed, successfully flown and manufactured. As a result, many designs and types of hang gliders can today be found on the market, of the monoplane as well as biplane type, of the tailless as well as of the tailed type, and some provided with directional control surfaces. Although the trend is towards gliders having higher aspect ratio wings, which in turn has resulted in improved glide ratios thus resulting in soaring of longer duration and greater distance, launching without assist remains the principal obstacle to full enjoyment of the sport of hang gliding, as long as launching remains the timehonored method of running upwind down a slope, in order to gain critical flying speed. As long as the angle of the slope or hillside is greater than the gliding angle, the hang glider lifts itself into the air when its air speed reaches approximately 15 to 20 mph, and is thus able to glide to the bottom of the slope or hill, the pilot taking advantages of any lift provided by thermals or any ascending air currents caused by the wind blowing up the slope or the hillside to prolong his flight. Such a method of launching requires appropriate launching sites with appropriate hilly or mountainous terrain, which are not always available in the near vicinity.
Several methods and devices can be used to launch manned hang gliders from the ground, in order to permit soaring flights notwithstanding the absence of hills, dunes or mountains. Such launch assist methods or means include towing the hang glider behind a motor boat or a land motor vehicle, by means of a winch, or by means of a powered light aircraft. Hang gliders have also been launched at altitude from hot air balloons. Power assist for hang gliders such as small gasoline engine driving a conventional propeller, and even small low thrust jet engines have appeared on the market. Such power assists are attached to the hang glider and permit limited power flight to altitude, or cruising on power.
Towing a hang glider behind a motor boat or behind a land motor vehicle, and launching by means of a winch present many problems and limitations, the most important of which is a limit on the altitude which the hang glider can reach when launched by means of such assist. Launching from a hot air balloon is much less altitude limited but it is very expensive and requires special skills on the part of the hang glider pilot, as the launch is effected without air speed and consists in a vertical drop followed by a stall recovery. Providing a hang glider with an auxiliary power in the form of a small gasoline engine and propeller, or a jet engine, is also costly, and is considered by other flyers as a noisy and undesirable nuisance and somewhat of a heresy. When the engine is stopped, soaring, unassisted, becomes somewhat limited in view of the increase in gross weight due to the weight of the powerplant and the additional drag created by the propeller and the powerplant frontal area, and stalling and landing speeds are appreciably increased. As a result, power assisted hang gliders tend to evolve in the direction of uncertified light aircrafts, to the point that even landing gears for motorized hang gliders have now appeared on the market.
Although towing a high aspect ratio conventional glider or sail plane to altitude behind a light powered aircraft is a conventional method for rapidly launching a great number of gliders in succession, such method has very seldom been used for towing hang gliders, because of the many problems involved, the most important of which is the difference in speed ranges between a conventional hang glider and a light aircraft. The maximum air speed of the majority of hang gliders is much less than the minimum flying speed or take-off speed of the majority of light aircrafts. In other words, a light aircraft towing a hang glider takes off at an air speed which is beyond the maximum, or "never exceed" air speed, to say nothing of the maximum maneuvering air speed, of the hang glider.
The present invention provides a powered towing aircraft which enables a hang glider to be towed to altitude and launched from such altitude over any kind of terrain, including flat ground. The towing aircraft of the invention provides an adequate thrust for take-off and climb to altitude with a hang glider in tow, has a low minimum air speed matching the hang glider minimum air speed, and a climb air speed and climb rate closely matching those of a conventional hang glider, is pilotless but highly controllable, does not place any excessive demand on the flying ability of the pilot of the towed hang glider, and provides at least a level of safety comparable to other means of launching a hang glider, such as by means of a winch, or by towing behind a land or a water vehicle.
The minimum thrust required for enabling a hang glider with its pilot to maintain flight, with enough reserve power for a moderate rate of climb, in a standard density and temperature day is in the neighborhood of 80 lbs. The thrust applied to a towed hang glider by a towing aircraft must therefore be at least 80 lbs. and preferably have a value of around 100 lbs. Most conventional hang gliders have a practical air speed range of about 16-20 mph minimum to about 35-45 mph maximum. The towed climbing speed for hang glider is therefore in the range of approximately 25 to 30 mph, and therefore the minimum air speed of a towing aircraft for a hang glider should not be greater than about 25 mph, and the towing aircraft must be fully controllable at such a low speed. A climbing speed, slightly above the take-off speed, must be maintained to altitude, under control, in order not to overstress the structure of the hang glider and its pilot's ability to cope with excessive demands upon his flying skill.
All those requirements are fulfilled by the present invention, and furthermore the present invention provides a reasonable amount of safety in view of the fact that the towing aircraft is pilotless and that disconnect between the towing aircraft and the towed hang glider is under the control of the hang glider pilot who can always safely disconnect and make a relatively normal landing irrespective of what may happen to the towing aircraft.